This invention relates to a method of selecting the operating mode of an electronic scale of the type for measuring weights of articles and for computing and displaying the cost of the articles and the number thereof, based on the measured weight, which method allows the operation of the scale to be checked with facility. The invention further relates to an electronic scale which uses the aforementioned method.
Scales which basically are for weighing articles have undergone remarkable technological advancements in recent years and now are capable not only of weighing but also of computing the cost of a batch of articles as well as the number of individual articles among articles of the same shape, provided that the scale is supplied with inputs of unit price and unit weight. Scales having the foregoing capabilities are referred to as electronic scales and have an input device such as a keyboard as well as arithmetic circuitry. The external appearance of such an electronic scale is as shown in FIG. 1, in which (A) is a perspective view of the overall scale, (B) is an enlarged view of a display provided on the electronic scale, and (C) is an enlarged view of an operation panel also provided on the electronic scale.
As shown in FIG. 1(A), the electronic scale includes a main body 100 incorporating various control circuits, a weighing tray 101 provided on the main body 100 for receiving the articles to be weighed, and a display device 5 supported on a column 102 affixed to the main body 100. The front side of the main body 100 is provided with an operation panel 103 having an input device 1 and a power switch 104. The display device 5, shown in greater detail in FIG. 1(B), is composed of a weight display section 5a for displaying the measured weight of articles placed on the weighing tray 101, a unit price display section 5b for displaying a unit price entered by operating the input device 1, and a cost display section 5c for displaying a cost computed from the measured weight and set unit price. As shown in FIG. 1(C), the input device 1 of the operation panel 103 includes a ten-key arrangement of numeric keys from "0" to "9", as well as function keys marked "ZERO", "PRINT", "TARE", " UNIT PRICE", "." and "CL".
Reference will now be had to FIG. 2 to describe the basic function of the above-described electronic scale. The electronic scale comprises a weight sensor A for sensing the weight of articles placed in the weighing tray 101, an arithmetic device 2 including a weight computing unit B for computing true weight by subtracting the tare weight from the output of the weight sensor A, and a cost computing unit for computing cost by multiplying the true weight by a unit price, the display device 5 for displaying, e.g., unit price, tare weight and cost, and the input device 1 having the ten-key arrangement and function keys for providing the arithmetic device 2 and display device 5 with inputs of unit price and tare weight. The arithmetic device 2 is provided with a RAM (random access memory) for storing various data, and with a printer (not shown) having printing circuitry and a printing drum. The weight sensor A is equipped with an A-D converter (analog-to-digital) converter for converting a measured analog weight into a digital value.
An electronic scale of the above type, having a large number of components arranged in the manner described, is checked at the factory prior to delivery to make sure that all the components are operating normally. Similarly, if a complaint stemming from a malfunction or failure is received from a user, the components must also be checked to locate the source of the problem. In either case, items checked are as follows:
(1) Zero adjustment
This involves displaying the currently prevailing output produced by the A-D converter of weight sensor A while the weighing tray 101 is empty. The displayed value is then adjusted to give a weight reading of zero.
(2) Key reliability
All keys are checked to determine whether they function properly when pressed. Numeric keys, for example, are pressed to determine whether the corresponding numerical values appear on the display device 5. Each function key, on the other hand, is assigned a specific number in advance. When a function key is pressed, therefore, the proper number should appear on the display device 5.
(3) Display segments
The display device is checked to assure that the display segments for the numerals 0 through 9 light properly.
(4) RAM
The RAM in the microcomputer of the arithmetic device 2 is checked for malfunction.
(5) Printing drum
The characters (printing type) on the printing drum are checked for flaws.
(6) Print driver
The printing circuitry is checked for defects.
(7) Display driver
The display circuitry is checked for defects.
(8) Display brightness
This involves checking the brightness of the display device.
According to the prior art, checking an electronic scale for the aforesaid items entails providing the scale with a special start switch, externally connecting a read-only memory (ROM) to the arithmetic device of the electronic scale, which ROM contains a stored test program for checking purposes, and turning on the start switch so that the arithmetic device may execute the test program stored in the ROM. For example, once an operating mode based on the test program has been initiated, the check for item (1) may be executed by pressing the numeric key marked "1", the check for item (2) by pressing the numeric key marked "2", and so on.
With the foregoing conventional method, the electronic scale must be specially provided with the start switch. Another disadvantage is that the ROM must be connected to the scale, making it difficult for an ordinary user to perform the check himself. The procedure can be troublesome even for a skilled dealer.